The present invention relates to a protection arrangement for a current collector on an electric vehicle. The protection arrangement is suitable for electric vehicles and hybrid vehicles having a rechargeable battery.
The share of partly or only electrically driven vehicles is expected to increase radically in the next 10 to 20 years. Such vehicles are normally referred to as electric vehicles and hybrid vehicles. This also means a corresponding increase in the need to charge such vehicles. In principle, the charging is done by connecting the vehicle to the electrical network, either directly to one of the ordinary outlets used for other equipments, or through a special charger, external to the vehicle. Charging current is transferred from the network to a battery on board the vehicle.
The battery of the electric vehicle may either be charged with a relatively low current over a relatively long time period, e.g. over night. Such vehicles are referred to as plug-in vehicles and are common for hybrid vehicles which are provided with a battery having a relatively low capacity, such that the distance that the vehicle can travel on electric power is limited. When the battery is empty, or when additional power is required, the combustion engine is started. High current charging of plug-in vehicles is also possible. Since the vehicle is charged one or two times a day, a specific connector is used to connect the vehicle to the current source.
For vehicles that need to be charged several times a day, such as commercial vehicles, a connection by using a plug is not an efficient alternative. Instead, various types of current collectors are used, such as a moveable pantograph or a fixed current collector, where the corresponding current supply means is movable and contacts the fixed current collector. During charging, the current collector must of course be exposed to the corresponding current supply means in order to supply current to the battery. However, when the vehicle is driven or is not charging, the current collector should preferably be disconnected from the battery such that the battery voltage will not be present on the current collector. When the battery is disconnected from the current collector, it is safe for a service technician to work on or near the current collector. A further advantage of disconnecting the battery from the current collector is to prevent persons or objects to come in contact with the battery voltage, which is in the range of 300-600 volts or more.
One way of disconnecting the battery from the current collector is to use a power switch arranged between the battery and the current collector. Such a power switch must be able to break a short-circuit current between two current collectors connected to the battery poles for safety reasons. Such a switch is rather expensive.
Pantographs are known to be mounted on the roof of some rail vehicles to connect to an overhead conductor. In those cases, the return line is the rail. Pantographs may also be used by electric trolley buses. Such electric vehicles are constantly powered with electricity and do not have a chargeable battery as an additional power source. This means that the pantograph is not connected to any electric source when the pantograph is folded down, e.g. for service purposes. For a service technician, it is possible to work on the roof of such a vehicle without any specific safety arrangements.
U.S. Pat. No. 3,762,515 describes an apparatus for covering exposed, electrically conductive elements of a guideway following, electric vehicle. The brush assemblies of such a vehicle are covered by insulative shields when power is conducted to the elements from an external source and the vehicle is marshalling. In order for such a vehicle to be able to bridge different power circuits when e.g. passing a switch, the vehicle is provided with several brushes positioned at the front and at the rear of the vehicle. All brush assemblies are connected to each other and to the drive motor. Thus, when an external power source is connected to power the motor, the power is also applied to the brushes. The insulative shields covers the brushes outwards for preventing contact with the brushes by bystanders.
EP 1 270 313 A2 and EP 1 371 517 A1 discloses a protection shield for a current collector adapted to protect the current collector of a rail vehicle at a platform. The protection shield is arranged between the platform and the vehicle and prevents objects to touch the current collector from above.
These protection devices are all adapted for electric vehicles powered directly from an electricity network. They may work fine in some situations, but are not adapted for vehicles having a chargeable battery. Hence, there is room for improvements.
It is desirable to provide an improved protection arrangement for a current collector on an electric vehicle.
In a protection arrangement for a current collector arranged on a vehicle having an electric propulsion unit and a rechargeable electric energy storage, where the protection arrangement comprises a first protective state in which the current collector is covered by the protection arrangement and a second open state in which the protection arrangement allows contact between the current collector and a corresponding current supply means during charging of the energy storage, the protection arrangement is automatically opened from the protective state to the open state when the vehicle has reached a predefined charging position.
By this first embodiment of the protection arrangement for a current collector according to the invention, the protection arrangement will be opened automatically when the vehicle arrives at or has reached a charging position such that contact between the current collector and a corresponding current supply means is possible during charging of the electric energy storage of the vehicle. The rechargeable electric energy storage may be a battery or a super capacitor. When the electric energy storage is not charged, e.g. when the vehicle is not positioned at a charging station, the current collector will be covered by the protection arrangement. In this way, an accidental contact with the current collector by a service person will not be possible. It is of advantage that the protection arrangement is enclosed such that an operator can not touch the current collector. Preferably, the protection arrangement will stop an arm or a finger from passing through, and also a pointed object such as a screwdriver or the like such that maintenance can be performed close to the protection arrangement without the risk of touching the current collector. It is also an advantage to enclose the current collector in case of an accident, e.g. when the vehicle falls over on the side. The rescue party will be able to start working without the risk of touching the current collector and will not have to start by disabling the current collector before they can proceed. An enclosed current collector is also a security advantage should someone unauthorized climb up on the roof of the vehicle.
It is further advantageous to automatically open the protection arrangement when the vehicle reaches a predefined charging position. In this way, the current collector will be enclosed when the vehicle e.g. is travelling or is parked outside of the charging station. When the vehicle is at the charging station, in the predefined charging position, the protection arrangement can be opened automatically. The protection arrangement can e.g. be opened automatically when the vehicle enters a predefined charging area such that the protection arrangement is open when the vehicle stops at the charging position or when the vehicle has stopped at the charging position. The protection arrangement may e.g. be opened when an opening signal is issued. An opening signal may be issued separately or may be issued together with a charging signal.
The advantage of enclosing the current collector is that it is not necessary to use a disconnecting switch or circuit breaker between the electric energy storage and the current collector. A disconnecting switch is normally used to disconnect the current collector from the battery of a vehicle in order to make the current collector powerless. Due to the high voltage and the high current capacity of such a battery, there are rigorous safety regulations controlling how and when to perform service on the electrical system of such an electric vehicle. It may e.g. be prescribed that the current collector must have been disconnected for a certain amount of time before service work can start.
Further, a disconnecting switch that can handle the voltage and current of such a high voltage and high current battery is both heavy and expensive. The switch must not only be able to handle the current during normal use but also the short-circuit current in case of a shortcut between two adjacent current collectors. Thus, by removing the need of a disconnecting switch, a simple and cost-effective solution is obtained.
A further advantage is that the protection arrangement opens automatically when the vehicle is close to or at the charging position at the charging station. In this way, the charging process is simplified and the driver of the vehicle must not connect or disconnect the vehicle to and from the charging equipment. The protection arrangement may either open when the vehicle enters a predefined position, such as a charging zone, or when the vehicle is stopped at the predefined position and an opening signal is issued. The protection arrangement is further closed automatically when a closing signal is issued. The closing signal may be issued when the charging process is completed, when the vehicle starts moving, when the vehicle leaves the charging zone or when a person is in the vicinity of the current collectors.
The current collector may in one example be a pantograph that folds up to contact a conductor rail or conductor plate of some kind. Preferably, since the vehicle is a road vehicle provided with tires, there are two current collectors provided on the roof of the vehicle. When pantographs are used, they may be arranged either side by side or after each other in the driving direction of the vehicle. In either way, care must be taken when connecting the pantograph to the conductor rail such that each current collector contacts the corresponding conductor. With a pantograph, the protection arrangement is preferably a pivotable cover that opens upwards. The cover may e.g. be spring-loaded such that it is pushed open by the pantograph and swings back when the pantograph is retracted.
The protection arrangement is preferably opened automatically when a vehicle enters the charging zone in order to allow contact between the current collector and the corresponding current supply means. When the current collector is a fixed contact surface positioned on the roof, the cover may be opened by the corresponding current supply means that is movable in order to be able to contact the contact surface. The corresponding current supply means may be movable such that it can contact the current collector at the proper charging position, since it may be difficult to position the vehicle at the exact charging position by the driver. The cove may be a slidable cover that slides backwards when the vehicle enters the charging station or when an opening signal is issued. The cover may also be a dividable cover that is opened sideways when the vehicle enters the charging station or when an opening signal is issued.
The charging station is preferably a stationary charging station positioned e.g. at a terminus stop where the vehicle will wait until the next round trip starts. With a waiting time of e.g. 15 minutes, the battery may be charged enough when high-current charging is used. It is also possible to position a charging station at one or two intermediate stops along the trip in order to allow refresh charging. It is also possible to have a charging station at each stop which allows the electric energy storage to be charged enough to reach the next stop. In such a system, a relatively small battery or super capacitor may be used.
The cover may be opened by a pushing means arranged on the current supply means. Such a solution can be used when the vehicle enters the charging station such that the cover is opened at the same time as the current supply means approaches the contact surface. The cover may also be opened by an actuator when an opening signal is issued. Preferably, the cover is spring-loaded towards a closed state such that the cover is opened by the pushing means or the actuator and is released to the closed state by a release catch or the like. The actuator may be an electric means or a compressed air means, such as an electromagnetic actuator or an air actuated valve.